JPH0480068B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION The present invention relates to a method of preventing premature curing of silicone compositions and compositions made therefrom. More specifically, the present invention prevents premature curing of silicone hydride-containing compositions caused by residual Lewis acid by adding an effective amount of Lewis base. (a) vinyl group-containing base polymer, (b) organohydrodiene polysiloxane crosslinking agent, and (c)
Curable silicone compositions comprising noble metals or noble metal-containing hydroxylation catalysts are well known in the art and are described, for example, in Nelson, U.S. Pat. No. 3,284,406 and Modic, U.S. Pat. No. 3,436,366. There is. Recently, there has been a great deal of interest in fluorosilicone compositions. This fluorosilicone composition is based on the same addition cure chemistry as U.S. Pat. No. 3,284,406 and U.S. Pat. No. 3,436,366, but has good solvent resistance due to the inclusion of perfluoroalkylsiloxy units in the vinyl-containing base polymer. I got sex. Examples of fluorosilicone compositions are U.S. Pat. No. 4,029,629 to Jeram, U.S. Pat. No. 443,545, all of which are assigned to the same assignee as this application. Although all of the aforementioned compositions can be obtained by simply mixing the various ingredients together, these compositions can be
Most conveniently, it is prepared in two separate parts or packages and mixed at the time the composition is converted to a hardened, solid, elastic state. In the case of the above two-component formulation, it is convenient for the first package to contain some or all of the vinyl group-containing polysiloxane, the precious metal catalyst and the fine powder filler, and the second package to contain the single essential Containing as a component an organohydrodiene polysiloxane crosslinking agent, it is advantageous if the second package also contains a portion of the vinyl group-containing base polymer and a portion of the fine powder filler. Micropowder fillers typically include at least some types of fumed silica or treated fumed silica, both of which are known to contain silanol groups. Additionally, silanol-functional plasticizers may be included in silicone compositions, particularly condensation curable, room temperature vulcanizable silicone compositions. The curable silicone compositions described above may exhibit premature curing. This premature hardening can be dramatic, eg, hardening in a dough mixer, or subtle, eg, gradually increasing the viscosity of the composition to the point where processing is hindered. This early curing is particularly noticeable in the second component of the aforementioned two-component addition-curable composition.
Since the second component usually contains some type of vinyl group-containing polymer, it was thought that the early curing was due to the inclusion of the noble metal catalyst. The inventors now show that the real cause of premature curing is the Lewis acid catalyzed condensation reaction involving the organohydrodiene polysiloxane and silanol-containing components such as fillers and/or plasticizers. I found it. Lewis acid catalysts are e.g.
It is believed that it is formed in situ through the reaction of trace amounts of HCl and/or chlorosilane with the group metal used in the second component colorant. SUMMARY OF THE INVENTION It is an object of the present invention to provide curable silicone compositions that do not exhibit premature curing. Another object of the present invention is to provide a method for preventing premature curing of curable silicone compositions. Most broadly, the present invention provides an improved method of substantially eliminating premature curing of curable silicone compositions, i.e., adding an amount of Lewis base to said curable silicone composition to substantially neutralize any Lewis acid present. An improved method is provided comprising mixing with a silicone composition. Also provided are improved curable silicone compositions, ie, compositions containing an effective amount of Lewis base to substantially neutralize any Lewis acid present. DESCRIPTION OF THE INVENTION In accordance with the present invention, an improved method for substantially eliminating premature curing of curable silicone compositions is disclosed, which is effective to substantially neutralize Lewis acids present in curable silicone compositions. An improved method is provided comprising mixing an amount of Lewis base with the curable silicone composition. In accordance with another invention of the present application, there is provided an improved curable silicone composition, that is, an improved curable silicone composition comprising an effective amount of Lewis base to substantially neutralize the Lewis acid present in the curable silicone composition. A composition is provided. Although premature curing problems are most common with addition curable silicone compositions, they can occur with any curable silicone composition containing silicon-bonded hydrogen atoms and silanol groups. The addition-curable silicone composition includes (a) an olefin-containing polydiorganosiloxane, (b) an organohydrodiene polysiloxane crosslinking agent, and (c) a crosslinking agent that promotes crosslinking of the olefin-containing polydiorganosiloxane and the organohydrodiene polysiloxane. A composition comprising a noble metal or noble metal-containing hydrosilylation catalyst that is effective for. Olefin-containing polydiorganosiloxanes usually use vinyl groups as olefin groups;
and such polymers generally have a temperature of about 100 to
It is clear to those skilled in the art that it has a viscosity of 500,000 centipoise. Too hardened, tensile strength,
In order to avoid an elastomer having an adverse effect on tear resistance and elasticity, it is preferred that almost all of the vinyl groups be bonded to the terminal siloxy units of the polymer chain. When it is desired to obtain a solvent-resistant elastomer, due to the presence of perfluoroalkyl-containing siloxy units,
It will be clear to those skilled in the art that such properties are provided. Preferably, the perfluoroalkyl units are 3,3,3-trifluoropropyl units and are present in about 5 to 98 mole percent. The organohydrodiene polysiloxane may be any polysiloxane containing silicon-bonded hydrogen atoms. It will be clear to those skilled in the art that this includes both resinous and linear polymers. If a solvent resistant fluorosilicone composition is desired, the organohydrodiene polysiloxane also preferably contains perfluoroalkylsiloxy units. Any noble metal or noble metal-containing hydrosilylation catalyst known in the art can be used. Particularly preferred are platinum- and rhodium-based catalysts, which are effective in catalyzing reactions between silicon-bonded hydrogen atoms and silicon-bonded olefin groups and are freely miscible in silicone polymers. I can do it. The most preferred hydrosilylation catalysts include the platinum hydrocarbon complexes described in Ashby U.S. Pat. No. 3,159,601 and 3,159,662 and the platinum alcoholate catalysts described in Lamoreaux, U.S. Pat. There are platinum-containing catalysts of Karstedt, US Pat. No. 3,814,730 and Modic, US Pat. No. 3,516,946. Other hydrosilylation catalysts useful in this invention include silicone soluble complexes of the metals ruthenium, palladium, osmium and iridium. Preferably the catalyst is present at 10-150 ppm as metal. The above-mentioned addition-curable silicone composition may further contain other components depending on the use. More commonly used additional ingredients include reinforcing fillers such as fumed silica, precipitated silica, treated fumed silica, treated precipitated silica, bulking fillers such as calcium carbonate and quartz powder, MQ and MDQ reinforcing resins and plasticizers. There are silanol-containing materials such as mold release agents, mold release agents, and processing aids. Reinforcing fillers are known to have silanol groups bonded to the surface of filler particles, and fall within the scope of silanol-containing substances. For convenience, addition-curable silicone compositions are commonly sold to consumers as two-component or two-packages. The first package contains some or all of the conventional olefin-containing polydiorganosiloxane, hydrosilylation catalyst, and filler. The second package, as a single essential component,
Although containing an organohydrodiene polysiloxane, the second component conveniently also typically contains a portion of an olefin-containing polydiorganosiloxane, a silanol-containing plasticizer or processing aid, and a portion of a filler. In selecting the components of each package, it is best if the hydrosilylation catalyst and the organohydrodiene polysiloxane are not included in the same package. Other variations of multicomponent systems will be apparent to those skilled in the art. A particularly useful variation is derived from Eckberg, US Pat. No. 4,448,815. If a two-package system as described above is used, the two packages may simply be mixed in any suitable manner at the point of use, and the mixture maintained at the curing temperature until curing is complete. Details for curing the composition will vary depending on the application and are well known in the art. Sometimes the second, i.e., organohydrodiene polysiloxane-containing component exhibits premature curing. This premature hardening can be dramatic, such as hardening in a dough mixer, or subtle, such as a gradual increase in viscosity until processing is no longer possible before use. It has now been discovered that the premature curing is caused by Lewis acids that catalyze the condensation reaction between the organohydrodiene polysiloxane crosslinker and silanol-containing components such as fillers, plasticizers or processing aids. Ta. It is believed that the Lewis acid is formed in situ by the reaction of trace amounts of HCl and/or chlorosilane with a group metal such as those used in the hydride-containing second component colorant. Having discovered the cause of premature curing, the inventors have decided to add to the composition, and in particular to the hydride-containing component of the composition, an amount of Lewis base effective to substantially neutralize the Lewis acid. I was able to solve the problem. Although any Lewis base can be added to the curable silicone composition, it is preferred that the Lewis base is an oxide of a Group 2A or Group 2B metal. More preferably, the Lewis base is selected from the group consisting of magnesium oxide, calcium oxide, barium oxide and zinc oxide, most preferably selected from the group consisting of magnesium oxide and calcium oxide. Of course, mixtures of any of the foregoing also fall within the scope of the invention and claims. In the practice of this invention, it has been found that an effective amount of Lewis base is generally from about 0.05 to about 3.0 parts by weight of the total composition or, in the case of a two-package version, the package containing the hydride and silanol.
Since the presence of an excess of Lewis base adversely affects the heat aging of the cured composition, the Lewis base should be between about 0.15 and about
Preferably, 2.0 parts by weight is used, more preferably about 0.2 to 0.5 parts by weight. Those skilled in the art will appreciate that it is important to thoroughly mix the Lewis base with the curable silicone composition to avoid isolated pockets of premature curing caused by areas having high concentrations of Lewis acid. It's obvious. Although the present invention has been described with respect to addition-curable silicone compositions, it is understood that the present invention contemplates the addition of Lewis bases to any curable silicone composition containing hydride and hydroxyl moieties. . Thus, it is within the scope of the present invention to add a Lewis base to the compositions described in US Pat. No. 3,888,815, for example when the silanol-containing base polymer component also includes a hydride-containing material. Of course, the invention does not apply if an acid condensation catalyst is intentionally used. The method of the present invention comprises mixing a curable silicone composition containing a hydride and a hydroxyl moiety with an amount of a Lewis base effective to substantially neutralize the Lewis acid present in the curable silicone composition. Become.
Of course, if the curable silicone composition is provided to the consumer in a two-package format, the Lewis base is mixed with the package containing the hydride and hydroxyl moieties. To enable those skilled in the art to more easily practice the invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight unless otherwise noted. [Example] Example 1 A composition that is a representative example of the second package of a two-package type addition-curable silicone composition was heated at 25°C.
100 parts vinyl-terminated polydimethyl-3,3,3-trifluoropropylmethylsiloxane copolymer having a viscosity of about 20,000 cps and containing about 40 mole percent fluorosiloxy-containing units, 16 parts silazane-treated fumed silica, silazane 21 parts of treated Zeothix 95, 5 parts of 10 micron Minusil®, 5 parts of a liquid fluorosilicone with a vinyl end group at one end of the polymer chain and a methyl end group at the other end; It was prepared by mixing 5 parts of silanol-containing liquid fluorosilicone, 3.4 parts of group metal-containing color masterbatch, and 1.9 parts of organohydrodiene polysiloxane crosslinking agent. A small amount of FeCl ₃ was thoroughly mixed into a portion of this representative second package of a two package system. Half of the composition was also thoroughly mixed with an approximately equal amount of magnesium oxide. Immediately, the composition containing only FeCl ₃ began to harden, whereas the composition containing both FeCl ₃ and MgO did not show premature hardening. This example illustrates the suitability of Lewis bases to prevent premature curing caused by Lewis acids. Example 2 This example demonstrates that the presence of preferred amounts of Lewis base does not adversely affect the properties of the cured composition. The first package of the two-package addition-curable silicone composition was prepared by removing the color masterbatch and organohydrodiene polysiloxane from the composition of Example 1 and replacing them with 0.1 part of platinum complex hydrosilylation catalyst and mylene. acid diallyl
It was prepared by replacing 0.1 part. to each representative sample of the second package;
MgO 0.25 parts, MgO 2.0 parts, CaO 0.25 parts, CaO
Added 2.0 parts. The first and second packages were then mixed in a 1:1 ratio and cured to form a silicone elastomer having the physical properties shown in Tables 1-3.

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【table】

TABLE The foregoing results demonstrate that the presence of an effective amount of Lewis base does not adversely affect the physical properties of the cured composition.

Claims (1)

[Scope of Claims] 1 (a) () A first package containing () an olefin-containing polydiorganosiloxane and () a noble metal or a noble metal-containing hydrosilylation catalyst, and (b) () containing an organohydrodiene polysiloxane crosslinking agent. In the curable silicone composition comprising the second package, in order to substantially neutralize the Lewis acid generated and present in situ in the second package, a Lewis base of 0.05
3.0 parts by weight of a curable silicone composition, characterized in that the second package contains 3.0 parts by weight. 2. The composition of claim 1, wherein the second package of the curable silicone composition further contains a silanol-containing material. 3. The composition of claim 3, wherein the addition-curable silicone composition is a fluorosilicone composition. 4. The composition according to claim 1 or 2, wherein the Lewis base is an oxide of a Group 2A or Group 2B metal. 5. The composition of claim 4, wherein the Lewis base is selected from the group consisting of magnesium oxide, calcium oxide, barium oxide and zinc oxide. 6. The composition of claim 4, wherein the Lewis base is selected from the group consisting of magnesium oxide and calcium oxide. 7. A composition according to claim 1 or 2, wherein the Lewis base is present in an amount of 0.15 to 2.0 parts by weight. 8. A composition according to claim 1 or 2, wherein the Lewis base is present in an amount of 0.2 to 0.5 parts by weight. 9 (a) () a first component containing an olefin-containing polydiorganosiloxane and () a noble metal or a noble metal-containing hydrosilylation catalyst; and (b) () an organohydrodiene polysiloxane crosslinking agent; () containing at least one silanol. a second component comprising: () 0.05 to 3.0 parts by weight of a Lewis base to substantially neutralize the Lewis acid generated and present in the second component; A curable silicone composition consisting of the following ingredients: